Given nothing more than some integer $m =$ OAEP($M$), is it possible to recover the original plaintext $M$? In other words, without being given the hash functions or the random string used for encoding, or even the length of it.

EDIT: This is being used in tandem with RSA, but I don't know the hash functions that OAEP usually uses with RSA; they might be public, for all I know.